1. Field of the Invention
This invention relates to laminates comprising a layer of a conductive polymer composition and an electrode in contact with the layer, and to methods and apparatus for making such laminates.
2. Summary of the Prior Art
Conductive polymer compositions (i.e. compositions comprising at least one polymer and electrically conductive particles dispersed in said polymer in amount sufficient to render the composition electrically conductive) are well known. Such compositions have been used in electrical devices which comprise at least one element composed of a conductive polymer composition and at least one electrode in contact with that element. Particularly useful devices of this kind comprise an element composed of a conductive polymer composition which exhibits positive temperature coefficient (PTC) behavior, and at least two electrodes which can be connected to a source of electrical power and which when so connected cause current to flow through the PTC element; the electrodes can be in direct physical contact with the PTC element or physically separated therefrom, e.g. by an element composed of a conductive polymer composition which exhibits relatively constant wattage behavior. When the conductive polymer composition is in the form of a layer, improved performance is often obtained when the electrode is in the form of a sheet, e.g. a tape or a section cut from a tape, often a sheet which is coextensive with the conductive polymer layer and/or has a plurality of openings therein. Reference may be made for example to U.S. Pat. Nos. 2,978,665 (Vernet et al), 3,243,753 (Kohler), 3,311,862 (Rees), 3,351,882 (Kohler et al) and 4,017,715 (Whitney et al) and copending and commonly assigned Applications Ser. Nos. 601,638 (Horsma et al), now U.S. Pat. No. 4,177,376, 750,149 (Kamath et al), now abandoned, 751,095 (Toy et al), now abandoned, 798,154 (Horsma), now abandoned, 873,676 (Horsma), 943,659 (van Konynenburg), now abandoned, 965,343 (van Konynenburg et al), 965,344 (Middleman et al) and 965,345 (Middleman et al), now abandoned, the disclosures of which are incorporated herein by reference.
Although, as noted above, the prior art refers to laminates comprising a layer of a conductive polymer composition and a sheet electrode in contact therewith, the known methods for producing such laminates suffer from serious disadvantages; for example discontinuous molding methods are slow and expensive and continuous lamination methods lead to products of inconsistent performance and/or are wasteful of the polymer composition.